Subsea field development wells are often drilled in a pattern that spaces the wells apart from each other. Some wells, particularly those in deeper water have production trees that connect to flowlines or jumpers that extend along the sea floor. The flowline jumpers lead to manifolds and/or to other subsea production trees. The flowline connector for each tree is often configured horizontal and off to one side of the tree.
When developing the field, the operator orients the trees to align with the flowline connectors. The operator typically precisely measures the various distances from connector to connector and prefabricates the jumpers. Sometimes after some of the wells have been drilled, plans change. The relative bearings between wells to be drilled may not be the same as originally anticipated. A change in plans may require reconfigured jumpers to match the revised placement of manifolds.
A typical subsea wellhead assembly has a high pressure wellhead housing supported in a low pressure wellhead housing and secured to casing that extends into the well. One or more casing hangers land in the high pressure wellhead housing, each casing hanger being located at the upper end of a string of casing that extends into the well. A string of tubing extends through the casing for conveying production fluids. A Christmas or production tree mounts to the upper end of the wellhead housing for controlling the well fluid.
One type of tree, sometimes called “conventional” or “vertical”, has two bores through it, one of which is the production bore and the other being the tubing annulus access bore. In this type of wellhead assembly, the tubing hanger lands in the high pressure wellhead housing. The tubing hanger has two passages through it, one being the production passage and the other being an annulus passage that communicates with the tubing annulus surrounding the tubing. Access to the tubing annulus is necessary, both to monitor and bleed down pressure during production and to circulate fluids down the production tubing and up through the tubing annulus, or vice versa, to either kill the well or circulate out heavy fluid during completion. The tree has isolation tubes that stab into engagement with the passages in the tubing hanger when the tree lands on the wellhead housing.
The tubing hanger for a conventional tree must be oriented in a desired direction before the tree is run. In this type of wellhead assembly, the low and high pressure wellheads are not oriented. Rather orientation is handled by running the BOP (blowout preventer) assembly on guidelines that orient the BOP to a guide base that supports the low pressure wellhead housing. The flowline connector is located on the guide base and fixed in a particular direction. The BOP assembly has an orientation pin within it. The tubing hanger has an orientation member that engages the internal orientation member of the BOP to orient the tubing hanger. The tree is also coarsely oriented typically by guidelines for aligning with the previously oriented tubing hanger, providing one tolerance path from the guidebase, via the BOP stack to the tubing hanger, and another from the guidebase to the tree, which must be accounted for.
In another type of tree, sometimes called “horizontal” tree, there is only a single bore in the tree, this being the production passage. The tubing hanger lands in the tree rather than in the high pressure wellhead housing. Neither the high nor the low pressure wellhead housing are oriented. The tree is oriented as it is lowered on the high pressure wellhead housing. The tubing hanger has a lateral port that requires orientation, thus it engages an orientation member in the tree as it is installed.
Flexibility within the installation of the overall subsea system (i.e. tree, flowline jumpers and manifolds) is desired for orienting trees in systems that locate the tubing hanger in the high pressure wellhead housing. For example, it would be useful to be able to change flowline connector orientation after the well has been drilled and cased, but before running the tubing hanger.